Pesticide treatment of soils or substates with sulphur compounds

ABSTRACT

In order to replace methyl bromide in all the uses thereof in soil or substrate treatment, the invention relates to the use of at least one sulphur compound having general formula: wherein R represents an alkenyl or alkyl radical, n is equal to 0, 1 or 2, x is a number between 0 and 4 and R′ represents an alkenyl or alkyl radical or, only if n=x=0, a hydrogen or alkali-metal atom. The sulphur compounds (in particular dimethyldisulphide) can be applied according to standard soil treatment methods (by injection, spraying, dripping, sprinkling) and said compounds have no phototoxic effects.

[0001] The invention relates to the field of agriculture and moreparticularly its subject is the replacement of methyl bromide in all itsuses for treating soils or plant substrates (compost, peat, rock wooland the like), in particular those intended for agriculture forcontrolling therein nematodes, pathogenic fungi, insect pests andbacteria.

[0002] Currently, the disinfection of soils or substrates, for examplethose intended for intensive agriculture and in particular thoseintended for aboriculture, horticulture and market gardening, ispredominantly carried out by fumigation with methyl bromide (worldconsumption greater than 70000 tons), this compound exhibiting in thegaseous state excellent nematicidal, fungicidal, insecticidal andbactericidal properties. Unfortunately, this compound contributes todepletion of the ozone layer and, in accordance with the Montreal accord(1992), by 2005 it should no longer be used in industrialized countries.There is therefore an urgent need to provide users with substituteswhich are equally effective and which are as environmentally friendly aspossible. In spite of the continuous efforts made both by governmentalorganizations and private bodies, no substitute has yet been found whichis capable, on its own and at the same cost, of replacing methyl bromidein all its uses with the same efficacy (cf. USDA Report, Vol. 6, No. 4and Citrus & Vegetable Magazine, Methyl Bromide Update: Spring 2000).Indeed, the main substitutes currently proposed are highly toxic andtherefore require respiratory protection which is expensive and not veryconvenient (case of dichloropropene) or their application is delicateand they therefore give variable results (case of Metam-sodium andtetrathio-carbonate) or they are considerably more expensive (case ofmethyl iodide).

[0003] To our knowledge, the only sulphur compounds envisaged assubstitutes for methyl bromide are methyl isothiocyanate (MITC),tetrathiocarbonate or MITC-generating compounds such as Metam-sodium andDazomet.

[0004] Despite the considerable efforts made by the scientific communitysince the banning of methyl bromide, few molecules have been found whichare capable of replacing it in its application in the fumigation ofsoils or of substrates although there are hundreds of pesticidesavailable (more than 700 nematicides, fungicides, insecticides,bactericides recorded in the Pesticide Manual, Tenth edition, Ed. CliveTombin). The reason is the need for fumigants to meet two essentialconditions: on the one hand, they should not exhibit, at the doses atwhich they are active, any phytotoxicity on the crops put in place afterthe treatment and, on the other hand, they should have the essential andrare property of not being completely absorbed into soils and ofdiffusing rapidly, in gaseous form, in the thickness of the soil to betreated, the pathogenic organisms being often present up to at least 50cm below the surface of the soil; furthermore, for obvious reasons ofproductivity, and in order to limit the risk of reinfestation, thetreatment time during which the fumigant acts should be as short aspossible.

[0005] A few scattered items of information exist in the literature onthe specific activity of certain sulphur-containing substances withrespect to various pathogenic organisms: that is the case for examplefor disulphides which prevent the larvae of nematodes from leaving thecysts (patent GB 249 830) or which act on insects of the coleoptera orlepidoptera type which are present in stored foodstuffs (Pestic. Sci.Vol. 55, 1999, pages 200-202); diallyl disulphides have a fungicidalaction on the sclerotia of S. cepivorum (Soil Biology and Biochemistry,Vol. 14, No. 3, pages 229-232); the nematicidal properties ofdisulphides or trisulphides derived from certain alliums on nematodes ofthe Meloidogyne incognita type are described in the article Agric. Biol.Chem. 52 (9) 1988, pages 2383-2385. The thiosulphinates (n=x=1) aredescribed in the literature as nematicides (JP 01 207 204), asfungicides and antibacterials (JP 57 075 906), as nematicides andantimicrobials (Agric. Biol. Chem., 1988, 52(9), pages 2383-2385), asinsecticides against the insects of stored foodstuffs (Pestic. Sci. Vol.55, 1999, pages 200-202). The insecticidal activity of the vapoursderived from ground products of allium containing, inter alia,disulphides and thiosulphinates has been demonstrated in PatentApplication FR-A-2 779 615 proposing the use of these ground productsfor the fumigation treatment of stored foodstuffs. However, for personsskilled in the art, it is a priori not obvious that a fumigant forstored foodstuffs may be suitable for application in the treatment ofsoils or substrates. Indeed, as explained in column 3 (lines 8-54) ofU.S. Pat. No. 5,518,692 recommending methyl iodide as a substitute formethyl bromide, soil is a much more complex medium than storedfoodstuffs (nonuniform moisture, particles of widely varying diameters,and the like) and the organisms to be controlled are a lot more numerousand varied in the case of soils. Consequently, most fumigants used forstored foodstuffs are not used for the fumigation of soils.

[0006] There is no information in the prior art on a global pesticidalactivity of these substances, that is to say a simultaneous nematicidal,fungicidal, insecticidal and bactericidal activity. The nematicidal,fungicidal and bactericidal activity of dimethyl polysulphides (having anumber of sulphur atoms greater than or equal to 3) is described in U.S.Pat. No. 2,917,429 but no mention is made of the insecticidal propertiesand dimethyl disulphide is reported as having a zero activity on a largenumber of fungi.

[0007] It has now been found that the sulphur compounds of generalformula:

[0008] in which R represents an alkyl or alkenyl radical containing from1 to 4 carbon atoms, n is equal to 0, 1 or 2, x is a number ranging from0 to 4, and R′ represents an alkyl or alkenyl radical containing from 1to 4 carbon atoms or, only if n=x=0, a hydrogen or alkali metal atom,are particularly advantageous for the fumigation of soils and substratesbecause they fulfil three essential conditions in order to be able to beused practically for disinfecting soils or substrates: they exhibitglobal pesticidal (nematicidal, fungicidal, insecticidal andbactericidal) properties: they are capable of rapidly diffusing in thethickness of the soil to be treated, giving a sufficient gasconcentration to kill the pathogenic organisms present; at the dosesnecessary for killing these pathogenic organisms, the compounds offormula (I) exhibit no phytotoxicity on the crops put in place after thetreatment. This set of essential properties for the applicationenvisaged has never been previously described for the compounds offormula (I).

[0009] As substitutes for methyl bromide, the compounds of formula (I)are all the more advantageous since some of them are already present innature, being derived from the natural degradation of crucifers andalliums. In particular, the thiosulphinates, included in general formula(I), are products which are naturally emitted when alliums are groundand, as such, they can be used in biological agriculture. Moreover,given that they do not contain halogen atoms which generate halogenatedradicals responsible for the catalytic destruction of the stratosphericozone, the compounds of formula (I) are without danger for the ozonelayer.

[0010] As nonlimiting examples of radicals R and R′, there may bementioned the methyl, propyl, allyl and 1-propenyl radicals. Among thecompounds of formula (I), the compounds for which n=0 are preferred.Other preferred compounds are the disulphides (n=0, x=1) and moreparticularly dimethyl disulphide (DMDS).

[0011] The compounds of formula (I) may be used in the pure state or invarious forms which, depending on the nature of the compound (I), may bean aqueous emulsion, a microemulsion, a product which ismicroencapsulated or supported by a solid, a solution in water, in anorganic solvent or as a mixture with a product which can itself have anactivity for the treatment of soils.

[0012] All these formulations may be prepared according to methods wellknown to persons skilled in the art. Thus, for example, the aqueousemulsions and the microemulsions may be obtained by adding one or moresurfactants to the compound of formula (I), and then in adding to themixture obtained a certain quantity of water so as to obtain a stableemulsion or a microemulsion.

[0013] Surfactants which are rather hydrophilic, that is to say thosehaving an HLB (“Hydrophilic Lipophilic Balance”) greater than or equalto 8, which may be of anionic, cationic, nonionic or amphoteric nature,are more particularly suitable for the preparation of the aqueousemulsions or microemulsions. As nonlimiting examples of anionicsurfactants, there may be mentioned:

[0014] alkali or alkaline-earth metal, ammonium or triethanolamine saltsof alkyl-, aryl- or alkylaryl-sulphonic acids, fatty acids with a basicpH, sulphosuccinic acid or alkyl, dialkyl, alkylaryl orpolyoxyethylenealkylaryl esters of sulphosuccinic acid,

[0015] alkali or alkaline-earth metal salts of esters of sulphuric,phosphoric, phosphonic or sulphoacetic acid and saturated or unsaturatedfatty alcohols, and their alkoxylated derivatives,

[0016] alkali or alkaline-earth metal salts of alkylarylsulphuric,alkylarylphosphoric or alkylarylsulphoacetic acids, and theiralkoxylated derivatives.

[0017] The cationic surfactants which may be used are, for example,those of the family of quaternary alkylammoniums, sulphoniums or fattyamines with acidic pH, and their alkoxylated derivatives.

[0018] As nonlimiting examples of nonionic surfactants, there may bementioned ethoxylated alkylphenols, ethoxylated alcohols, ethoxylatedfatty acids, fatty esters of glycerol or fatty derivatives of sugar.

[0019] The amphoteric surfactants which may be used are, for example,alkylbetaines or alkyltaurines.

[0020] The preferred surfactants for the preparation of the aqueousemulsions and microemulsions are compounds based on alkylbenzenesulphonate and alkoxylated alkylphenol.

[0021] The organic solvents which may be used to dissolve the compoundsof formula (I) according to the invention are hydrocarbons, alcohols,ethers, ketones, esters, halogenated solvents, mineral oils, naturaloils and their derivatives, and aprotic polar solvents such asdimethylformamide, dimethyl sulphoxide or N-methylpyrrolidone.Biodegradable solvents, more particularly methyl esters of rapeseedoils, are particularly suitable.

[0022] The products with pesticidal activity which are particularlysuitable for mixing with the compounds of formula (I) according to theinvention are pure products such as 1,3-dichloropropene or chloropicrin(Cl₃C—NO₂) which are themselves used as fumigants, aqueous solutions ofproducts such as Metam-sodium (CH₃—NH—CS₂ ⁻Na⁺) or sodiumtetrathiocarbonate (Na₂CS₄) which are also used as fumigants, or anyother product having an activity which is complementary to orsynergistic with the compounds of formula (I), such as MITC (CH₃—NCS) orDazomet (generator of MITC).

[0023] The compounds of formula (I) and the compositions containing themmay be applied according to any of the conventional methods forintroducing pesticides into the soil, such as, for example, injection bycoulters which makes it possible to introduce the product deep, sprayingon the soil, drip by a conventional irrigation system or “sprinkler”type sprinkling. After introducing the product into the soil andoptionally spreading (for example using a rotary spade in the case ofinjection into the soil), the surface of the soil may be optionallyclosed, either by capping the surface by means of a smoothing roller, orwith a plastic film.

[0024] The doses of compound (I) to be used in order to obtain thedesired effect are generally between 150 and 1000 kg/ha and depend onthe nature of the compound (I), the level of soil infestation, thenature of the pests and of the pathogenic organisms, the type of cropand soil, and the application methods. At these doses, the desiredgeneral pesticidal (nematicidal, fungicidal, insecticidal andbactericidal) effect and no phytotoxic effect is observed.

[0025] There-will be no departure from the scope of the presentinvention by combining the treatment with a compound of formula (I) witha treatment (simultaneous or otherwise) with one or more otherpesticidal substances.

[0026] The following examples illustrate the invention without limitingit.

EXAMPLE 1 Formulations EXAMPLE 1a

[0027] Aqueous emulsions having sufficient stability to allowhomogeneous application of the product to the soil after the preparationof the emulsion can be obtained by mixing:

[0028] 692 g of dimethyl disulphide, 38.5 g of Toximul® D, 38.5 g ofToximul° H (2 surfactants marketed by the company Stepan, based on alkylbenzenesulphonate and alkoxylated alkylphenol in alcoholic solution),and 9230 g of water: formulation A.

[0029] 1800 g of dimethyl disulphide, 160 g of Toximul® DH68, 40 g ofToximul® DM83 (2 surfactants marketed by the company Stepan, based onalkyl benzenesulphonate), and 8000 g of water: formulation B.

[0030] 1600 g of dimethyl disulphide, 320 g of Toximul® DH68, 80 g ofToximul® DM83 (2 surfactants marketed by the company Stepan, based onalkyl benzenesulphonate), and 8000 g of water: formulation C.

EXAMPLE 1b

[0031] A water-dimethyl disulphide microemulsion may be prepared byadding 4400 g of water to a mixture of 4400 g of dimethyl disulphide,960 g of Toximul® DH68 and 240 g of Toximul® DM83 (2 surfactantsmarketed by the company Stepan, based on alkyl benzenesulphonate):formulation D.

EXAMPLE 1c

[0032] A solution of dimethyl disulphide in rapeseed methyl ester, abiodegradable solvent which makes it possible to increase the flashpoint of the preparation to be applied and therefore to improve thesafety of the applicator, may be obtained by dissolving 3000 g ofdimethyl disulphide in 7000 g of rapeseed methyl ester: formulation E.

EXAMPLE 2 Phytotoxicity EXAMPLE 2a

[0033] The absence of phytotoxicity of dimethyl disulphide (DMDS)applied in the form of formulation A, in the dose range where it iseffective on pathogenic soil organisms, was demonstrated on youngcucumber plants (9 cm, 2 leaves, ARIS hybrid) and young tomato plants(13 cm, 3 leaves, JUMBO hybrid):

[0034] For both types of crop, 4 treatments were performed on 20 plants:

[0035] untreated control

[0036] 360 kg/ha of DMDS

[0037] 540 kg/ha of DMDS

[0038] 720 kg/ha of DMDS

[0039] Five days after the treatment, the young plants are transplantedinto pots 20 cm in diameter and 35 cm in height.

[0040] The observations relating to the number of leaves per plant andthe visual state of the plants are carried out 15 and 41 days after thetransplantation: TABLE 1 Average number of leaves per plant TomatoCucumber after 15 after 41 after 15 after 41 Treatment days days daysdays Untreated 5.5 9.7 5.4 9.8 control DMDS: 5.3 9.6 5.3 9.8 360 kg/haDMDS: 5.3 9.4 5.7 9.7 540 kg/ha DMDS: 5.7 9.8 5.7 9.9 720 kg/ha

[0041] The results of Table 1 show that there is no significantdifference between the untreated control and the plants treated withDMDS, regardless of the concentration tested; furthermore, no visualsymptom of phytotoxicity was detected.

EXAMPLE 2b Absence of Phytotoxicity on Lettuce of DMDS Applied at 150kg/ha, in the Open, in a Greenhouse

[0042] 1. Materials and Methods

[0043] Lettuce Variety: Sprintia

[0044] Treatment: DMDS is applied in the form of formulation A with theaid of a jet sprayer, and then incorporated over a depth of about 5 cmwith a rotary hoe. The soil is then covered with a black polyethylenefilm.

[0045] Planting: 7 days after the treatment, at the rate of 160000plants/ha

[0046] Harvesting: 2 months and 20 days after planting.

[0047] 2. Results

[0048] Visual observations on the field 1 and 2 months after plantingrevealed no sign of phytotoxicity. At harvest, the average weight of thelettuce treated with DMDS was measured and found to be equal to 505 g,compared with 490 g for the control with no treatment. It can thereforebe concluded that the treatment carried out with DMDS is withoutphytotoxic effect on lettuce.

EXAMPLE 3 Diffusion into the Soil

[0049] The rate of diffusion of DMDS was studied by filling a sealedthermal glass chamber of 3.3 litres and 40 cm in height with 2.5 litresof earth (that is 33 cm) obtained from the Garonne valley (sandy-muddysoil containing 1.6% of organic matter); the DMDS was deposited at thesurface of the earth in 2 doses: 300 and 800 kg/ha, that is, consideringa disinfection over 30 cm, doses of 100 and 266.6 g/m³ of soil. Thereare then measured by gas chromatography, as a function of time (inhours), the concentrations of DMDS in gaseous form (in g/m³) in the topfree volume of the chamber (point A) and at 11 cm (point B), 22 cm(point C) and 33 cm (point D) below the level of the earth by means of 3openings equipped with sealed septums on the side of the chamber; thevariation in the concentration as a function of time for the 4measurement points is thus obtained, as shown in Table 2 in the case ofthe 800 kg/ha does. TABLE 2 DMDS concentrations in g/m³ - case of the800 kg/ha dose Time in h A (0 cm) B (−11 cm) C (−22 cm) D (−33 cm) 0 0 00 0 1 144.9 76.6 3 0 3 152.7 73.9 5.1 0.3 5 96.3 63.8 48.4 21.5 5.5123.7 91.4 58.3 29.4 24 32.7 30.2 40.1 34.4 96 11.8 11.5 12.9 14.6

[0050] Table 2 shows that approximately 24 hours are sufficient for theDMDS concentration to be homogeneous in the entire thickness of thecolumn of earth.

[0051] The product CT of the concentrations C by the time of measurementT is another essential data which indicates the cumulative doses of DMDSto which are subjected the pathogenic organisms which may be present atthe different measurement points. The CT values in gh/m³ indicated inTable 3 are thus found for the two concentrations tested. TABLE 3 DosesA (0 cm) B (−11 cm) C (−22 cm) D (−33 cm) 300 kg/ha 3187 2737 2753 2210800 kg/ha 4145 3327 3276 2809

[0052] The CT values measured are therefore of the order of 2500 gh/m³for a dose of 300 kg/ha and 3000 gh/m³ for a dose of 800 kg/ha.

EXAMPLE 4 Fungicidal Properties

[0053] The fungicidal effect of DMDS was demonstrated on four of thecommon pathogenic organisms which are damaging to the principal marketgarden crops described in the article “Désinfecter les sols autrement”[Disinfecting soils differently] published in June 1999 in the CTIFL(Centre technique interprofessionnel des fruits et légumes) review.These four organisms are the following:

[0054]Phytophthora cactorum, one of the best known representatives ofthe Phytophthora family, polyphagous fungi which attack mainly tomato,sweet pepper and strawberry plants, these three crops representing themajority of the worldwide consumption of methyl bromide. Phytophthoracactorum, in particular, attacks mainly the strawberry plant and fruittrees.

[0055]Rhizoctonia solani: a very important group of polyphagouspathogens in the genus Rhizoctonia and which attack very many marketgarden crops including sweet pepper and lettuce.

[0056]Sclerotinia sclerotiorum: polyphagous fungus which attacks mainlymelon crops.

[0057]Sclerotium rolfsii: a fungus which is also polyphagous and whichis found, for example, on melon and courgette crops.

[0058] These four fungi were studied in the following form:

[0059]Sclerotinia sclerotiorum: sclerotia

[0060]Sclerotium rolfsii: sclerotia

[0061]Rhizoctonia solani: colonized barley grains (mycelium andsclerotia) Phytophthora cactorum: colonized millet grains (mycelium,sporangia and oospores)

[0062] Preparation of the Fungi (24 h Before the Gassing Operation)

[0063] 1. Preparation of the Sclerotia of Sclerotinia sclerotiorum andof Sclerotium rolfsii: The fungi are cultured on malt agar medium untilthe sclerotia are obtained. The sclerotia are collected in a sterilemanner and stored dry in empty Petri dishes until they are used. Thesclerotia used for the trial are over 3 months old and are perfectlydormant.

[0064] 2. Preparation of Phytophthora cactorum and of Rhizoctoniasolani:

[0065] The millet and barley used for the multiplication of the twofungi are moistened with ultrapure water by immersing for 24 hours. Thegrains are then slightly drained and then distributed into flasks andautoclaved (3 autoclavings at 110° C. for 20 minutes, 3 times at 24 hourintervals). Fragments of fungal culture are introduced into the flaskswhich are then incubated at 22° C±20° C. (white light 18 h) untilhomogeneous colonization is obtained. The grains are then removed fromthe flasks in a sterile manner, dried in the sterile stream of a safetycabinet and then stored in the dry state until they are used.

[0066] Conditions for Gassing and for Desorption

[0067] All the batches of fungi to be treated are placed for a few hoursat the trial temperature (20° C.). Between 35 and 300 units of fungi or“propagules” (grains or sclerotia) are subjected to gassing during eachtrial.

[0068] Each fumigation chamber comprising to one or more species offungi corresponds to a glass round-bottomed flask which is impervious tothe gas and has a volume of 11 litres. Each round-bottomed flask isequipped with branch connections, one at the bottom for introducing theliquid DMDS, one at the top for collecting the air sample with asyringe.

[0069] Before introducing the gas, a partial vacuum (−500 mbar) isestablished in the round-bottomed flask with a vacuum pump. This makesit possible, on the one hand, to avoid the phenomenon of excess pressuredue to the expansibility of DMDS in the round-bottomed flask and, on theother hand, to promote better homogeneity of the air-gas mixture in thefirst few seconds which follow injection. The DMDS (weighed accuratelyto the mg) is injected with a syringe, in liquid form, through thebottom branch connection, that is to say under the screen placed at halfheight of the round-bottomed flask and supporting the batches of fungi.After introducing the product, the internal pressure of theround-bottomed flask is re-established at atmospheric pressure. Amagnetic stirrer operates during the entire duration of the treatment inorder to properly homogenize the air-gas mixture.

[0070] At the end of the gassing, the cover for the round-bottomed flaskis removed. One minute after this operation, the batches of fungi gassedare taken out and left in the open air for 15 minutes for desorption ofthe DMDS. They are then transferred into a Petri dish, the latterremaining open for 5 minutes to allow perfect desorption of the gas.

[0071] Measurement of the Gas Concentrations

[0072] The mean concentration (C in g/m³) of DMDS in the fumigationchamber after homogenization of the gas in the chamber air is measuredby GC with an FID detector and, taking into account the duration ofexposure (T in hours), the product CT (g.h/m³) is calculated which, inthe field of fumigation, is the key parameter to be considered, sincethe biological efficacy of a gas towards a given pathogenic agent isonly effective if the latter was exposed to a certain mean concentrationC for a certain duration of exposure T, that is to say to a certainvalue of the product CT, a value (or dose) which can be reached indifferent ways: low concentrations and long duration of exposure orconversely.

[0073] Conditions for Reading the Results

[0074] Grains: After gassing, the grains are deposited on a selectivemedium in an amount of 5 to 10 per Petri dish of 90 mm (Rhizoctonia:Malt agar; Phytophthora: Malt agar+Pimaricin, Ampicillin, Rifampicin,Benomyl).

[0075] Sclerotia: After gassing, the sclerotia are superficiallydisinfected with Javel water (1% NaOCl), rinsed twice with sterilewater, and then deposited in an amount of one per dish on a maltagar-chloramphenicol medium (200 ppm).

[0076] Expression of the Results

[0077] The number of propagules giving rise to a colony (viablepropagules) are noted daily until there are no changes, and at most 19days after the day of gassing.

[0078] The results are expressed as:

[0079] viability (V), that is to say the percentage of viable propagulesgiving rise to a colony

[0080] reduction in viability (Rv) compared with the control, that is tosay: $R_{v} = {\frac{V_{control} - V}{V_{control}} \times 100}$

[0081] vitality score (Nm): to each propagule which has given rise to acolony, a score (N) is attributed which describes how fast thispropagule develops; this score, equal to the difference between thetotal number of days of observation (19 maximum) and the number of daysbetween depositing in a Petri dish and the development of the colony, ishigher, the closer the appearance of the colony to the date ofdepositing in a Petri dish. For each of the trials, a mean (Nm) of thescores attributed is then calculated.

[0082] reduction in vitality score (R_(Nm)) compared with the control,that is to say:$R_{Nm} = {100 - {\frac{Nm}{{Nm}_{control}} \times 100}}$

[0083] Results

[0084] 1. Biological Efficacy of DMDS on Phytophthora cactorum

[0085] The results assembled in Table 4 clearly show that, at CT dosesgreater than 2500 g.h/m³ approximately, the fungicidal efficacyprogresses regularly with the CT dose: reduction in viability andvitality score. Total efficacy (0% viability) is obtained at about 3500g.h/m³. TABLE 4 Summary of all the readings expressed in terms ofviability and vitality on Phytophthora cactorum (X = number of grains)Vitality Viability Nm (over X C T CT V RV 12 days) RNm 60 17.46 24 41991.7 6.8 7.7 15.5 60 26.04 24 625 100 −1.7 8.05 11.9 60 29.29 24 703 100−1.7 8.3 9.1 60 37.79 24 907 100 −1.7 7.2 21.2 60 15.91 66 1 050 95 5.05.5 43.1 90 21.24 66 1 402 97.8 2.2 6.6 32.2 60 30.96 48 1 450 95 3.45.4 40.7 90 28.77 66 1 899 97.8 2.2 5.6 42.6 90 30.02 66 1 981 97.8 2.25.3 45.7 60 51.25 48 2 460 43.3 55.9 1.7 81.2 300 37.44 66 2 471 nm* nm*nm* nm* 90 42.98 66 2 837 16.7 83.3 0.6 93.6 300 45.06 66 2 974 nm* nm*nm* nm* 90 48.02 66 3 169 1.1 98.9 0.05 99.5 300 52.53 66 3 467 0 100 0100

[0086] 2. Biological Efficacy of DMDS on Rhizoctonia solani

[0087] The results assembled in Table 5 clearly show that at CT dosesgreater than 2000 g.h/m³ approximately, the fungicidal efficacyprogresses regularly with the CT dose: reduction in viability andvitality score. Total efficacy (0% viability) is obtained at about 3500g.h/m³. TABLE 5 Summary of all the readings expressed in terms ofviability and vitality on Rhizoctonia solani (X = number of grains)Vitality Viability Nm (over X C T CT V RV 11 days) RNm 60 17.46 24 419100 0 9.0 0 60 26.04 24 625 100 0 8.7 3.1 70 29.29 24 703 100 0 8.3 7.370 37.79 24 907 100 0 7.1 21.6 65 15.91 66 1 050 89.2 10.8 7.0 22.2 6521.24 66 1 402 96.9 3.1 7.6 15.0 65 30.96 48 1 450 98.5 1.5 4.4 51.3 7028.77 66 1 899 84.3 15.7 6.0 33.2 75 30.02 66 1 981 94.7 5.3 7.4 17.2 7351.25 48 2 460 11.0 89.0 0.3 96.2 286 37.44 66 2 471 24.1 75.9 0.6 92.090 42.98 66 2 837 2.2 97.8 0.1 98.4 286 45.06 66 2 974 9.4 90.6 0.1 98.480 48.02 66 3 169 1.2 98.8 0.05 99.3 290 52.53 66 3 467 0 100 0 100

[0088] 3. Biological Efficacy of DMDS on Sclerotinia sclerotiorum

[0089] The results assembled in Table 6 clearly show that at CT dosesgreater than 1000 g.h/m³ approximately, the fungicidal efficacyprogresses regularly with the CT dose:reduction in viability andvitality score. Total efficacy (0% viability is obtained at about 3500g.h/m³, considering that the point CT 3467 is an abnormal point. TABLE 6Summary of all the readings expressed in terms of viability and vitalityon Sclerotinia sclerotiorum (X = number of grains) Vitality Viability Nm(over X C T CT V RV 19 days) RNm 39 17.46 24 419 89.7 −3.0 13.3 −3.6 4126.04 24 625 87.8 −0.8 12.8 0.1 41 29.29 24 703 85.4 2.0 12.6 2.2 3837.79 24 907 81.6 6.3 12.0 6.6 67 15.91 66 1 050 41.8 56.1 5.1 63.6 6221.24 66 1 402 46.8 50.9 1.3 90.6 47 30.96 48 1 450 29.8 65.8 1.0 92.164 28.77 66 1 899 29.6 68.9 3.6 74.8 54 30.02 66 1 981 20.3 78.7 2.781.2 41 51.25 48 2 460 14.6 83.2 0.7 94.9 170 37.44 66 2 471 32.9 67.14.6 70.5 64 42.98 66 2 837 14.1 85.2 1.8 87.5 170 45.06 66 2 974 11.288.8 1.6 89.9 64 48.02 66 3 169 0 100 0 100 170 52.53 66 3 467 32.3 67.73.3 79.0

[0090] 4. Biological Efficacy of DMDS on Sclerotium rolfsii

[0091] The results obtained are assembled in the following Table 7. Forthis fungus, a slight deterioration in the quality of the inoculum wasobserved over time. Nevertheless, the visibility and the vitality aregreatly affected from CT values of 900 to 1000 g.h/m³ and total efficacyis obtained between 2000 and 2500 g.h/m³. TABLE 7 Summary of all thereadings expressed in terms of viability and vitality on Sclerotiumrolfsii (X = number of grains) Vitality Viability Nm (over X C T CT V RV19 days) RNm 44 17.46 24 419 59.1 33.7 5.1 40.9 41 26.04 24 625 53.739.8 4.8 44.3 37 29.29 24 703 51.4 42.4 4.4 48.7 37 37.79 24 907 16.281.8 1.4 84.2 58 15.91 66 1 050 27.6 68.0 2.1 71.1 60 21.24 66 1 40218.3 78.7 1.3 81.8 40 30.96 48 1 450 15.0 83.2 0.7 91.8 65 28.77 66 1899 3.1 96.4 0.2 96.8 70 30.02 66 1 981 4.3 95.0 0.3 95.1 40 51.25 48 2460 10.0 88.8 0.4 94.7 170 37.44 66 2 471 0 100 0 100 90 42.98 66 2 8370 100 0 100 170 45.06 66 2 974 0 100 0 100 80 48.02 66 3 169 0 100 0 100170 52.53 66 3 467 0 100 0 100

[0092] In summary, for the four species of fungi studied, DMDS causes amarked decrease in the population from CT doses of between 2000 and 2500g.h/m³, or even at around 1000 h/m³ in the case of Sclerotinia andSclerotium, and total mortality for CT doses of between 3000 and 3500g.h/m³, or even between 2000 and 2500 g.h/m³ for Sclerotium.

EXAMPLE 5 Nematicidal Properties

[0093] The nematicidal effect of dimethyl disulphide (DMDS), dipropyldisulphide (DPDS) and diallyl thiosulphinate (allicin), three majordegradation products of allium, was demonstrated by in vitro testscarried out on larvae of Meloidogyne arenaria, a species among the rootgall nematodes, which are highly noxious and extremely polyphagous andamong the most widespread worldwide, on most vegetable crops, inparticular those of tomato and strawberry plants which are the cropswhich consume the most methyl bromide.

[0094] Materials and Methods

[0095] The second-stage juvenile larvae (the free and infesting stage)are immersed for 24 hours in the test solution and then the number oflarvae paralysed are counted before transferring them into pure waterfor another 24 hours. At the end of the 48 hours which have thuselapsed, the larvae paralysed are again counted and the larvae trulydead are counted the next day.

[0096] The breeding of the nematodes was carried out on tomato plants.The tests were carried out with aqueous solutions of DMDS at 0.0001%,0.1%, 1% and 5% by mass, of DPDS at 1%, 5% and 10% by mass, and ofallicin at 0.0003%, 0.0015% and 0.003% by mass, compared with a controlconsisting of pure water, and repeated five times. The ovicidal activitywas also evaluated according to the same modalities, by counting thenumber of hatchings after 5 to 20 days following exposure to theproducts.

[0097] Results

[0098] At a concentration of less than 1%, DMDS has only a very weaknematostatic activity and no nematicidal activity.

[0099] At a concentration of greater than or equal to 1%, DMDS and DPDSexhibit a high nematostatic and nematicidal activity, as clearly shownin Tables 8 and 9. Total efficacy (100% mortality) is obtained forconcentrations of greater than or equal to 1% in the case of DPDS.

[0100] Allicin also exhibits a high nematostatic and nematicidalactivity at much lower concentrations as shown in Table 10. However,total efficacy (100% mortality) was not evaluated in this case. TABLE 8Efficacy of dimethyl disulphide (DMDS) on the larvae ConcentrationImmobility rate Immobility rate Mortality rate by mass (%) after 24 h(%) after 48 h (%) after 72 h (%) 0 (control)  8  6  9 1 72 84 80 5 9798 98

[0101] TABLE 9 Efficacy of dipropyl disulphide (DPDS) on the larvaeConcentration Immobility rate Immobility rate Mortality rate by mass (%)after 24 h (%) after 48 h (%) after 72 h (%) 0 (control)  8  7  9 1 89100 100 5 93 100 100 10  95 100 100

[0102] TABLE 10 Efficacy of allicin on the larvae ConcentrationImmobility rate Immobility rate Mortality rate by mass (%) after 24 h(%) after 48 h (%) after 72 h (%) 0 (control)  2 10  8 0.0003  7 49 120.0015 19 85 45 0.003  49 65 63

[0103] As is evident from Tables 11 and 12, DMDS and DPDS also show avery high ovicidal activity. In both cases, an approximately 97%reduction is observed in the number of hatchings on the last day ofobservation. TABLE 11 Efficacy of DMDS on the eggs of nematodesConcentration Number of hatchings (cumulative) by mass (%) D5 D10 D13D17 0 (control) 141 179 184 184 1 7 7 7 7 5 2 2 5 5 10  0 2 5 5

[0104] TABLE 12 Efficacy of DPDS on the eggs of nematodes ConcentrationNumber of hatchings (cumulative) by mass (%) D5 D8 D12 D15 D19 (0)control 550 810 990 1 030 1 030  1 117 183 200   200   200  5 67 67 67  67   67 10 33 33 33   33   33

EXAMPLE 6 Insecticidal Properties

[0105] The insecticidal activity of dimethyl disulphide (DMDS), ofdiallyldisulphide (DADS) and of diallyl thiosulphinate (allicin) wasdemonstrated by in vitro tests on a soil insect, a termite(Reticulitermes santonensis).

[0106] Materials and Methods:

[0107] Dead wood infested with termites was collected from the soil onground occupied by a colony. This dead wood serves as breeding medium.The breeding is maintained at a constant 25° C. and a day/night 12:12alternation.

[0108] The insects are removed in an amount of 2 soldiers per 28workers.

[0109] The tests are carried out in hermetically closed glass jarshaving a volume of 3 L and containing the insects.

[0110] The product to be tested is introduced through a hole 2 mm indiameter with the aid of a micropipette and deposited on a filter paper(2×5 cm: Whatman No. 1) suspended at the centre of the jar where itmigrates by capillarity and vaporizes rapidly. The hole is hermeticallyclosed again as quickly as possible.

[0111] The jars are placed for 24 hours in an incubator under the samebreeding conditions.

[0112] At the end of 24 hours, after a few instants of aeration, a firstcount is made and then the insects are placed again under breedingconditions for another 24 hours. The counting of the mortality istherefore carried out at the end of 48 hours. It is this final countwhich will serve to calculate the LCSO at 24 hours of fumigation, thefirst being only an indication of the variation post-treatment. Indeed,numerous fumigants have a “knock down” effect which can suggest deathfor insects which prove to be alive on the next day after recovering.Each test is carried out on a population of 30 to 50 insects and isaccompanied by a control without treatment. Several repeats are carriedout with doses close to the LC50. TABLE 13 Results (Probits method) DMDSDADS Allicin LC50 in g × 24 h/m³ 0.095 0.011 0.010

[0113] Conclusion:

[0114] As indicated in Table 13, the 3 products tested show an excellentinsecticidal activity on the insect in the soil used. The activity ofDADS, which is close to that of allicin, is greater than that of DMDS,which is itself comparable to that of methyl bromide (0.1×24 h/m³).

EXAMPLE 7 Effects on Microorganisms

[0115] The effect of DMDS, applied at 150 kg/ha in the form offormulation A, to soil microorganisms was evaluated according to thefollowing standard methods:

[0116] “Recommended tests for assessing the side-effects of pesticideson the soil micro flora”, Technical Report Agricultural Research CouncilWeed Research Organization, 1980 (59).

[0117] “OECD Guideline for Testing of Chemicals—Soil Microorganisms:Carbon Mineralization Test”, Draft document, June 1996.

[0118] The effect of DMDS on soil microorganisms is measured by thereduction in the oxygen consumed by these microorganisms, expressed inmg 02 per kg of dry soil per h, 14, 28, 42, 57 days after the treatment(Table 14). TABLE 14 Day 0 Day 14 Day 28 Day 42 Day 57 Untreated control11.23 10.18 7.87 9.12 7.30 DMDS 150 kg/ha 9.70 8.74 6.62 8.93 4.90

[0119] Table 14 shows a significant reduction in the oxygen consumed bythe microorganisms, attributed to a reduction in their population.

1. Pesticidal (nematicidal, fungicidal, insecticidal and bactericidal)treatment of soils or substrates, preferably by fumigation,characterized in that there is applied to the soil or in the substrateat least one sulphur compound of general formula:

in which R represents an alkyl or alkenyl radical containing from 1 to 4carbon atoms, n is equal to 0, 1 or 2, x is a number ranging from 0 to4, and R′ represents an alkyl or alkenyl radical containing from 1 to 4carbon atoms or, only if n=x=0, a hydrogen or alkali metal atom. 2.Treatment according to claim 1, in which the radicals R and R′ of thecompound(s) of formula (I) are chosen from methyl, propyl, allyl and1-propenyl radicals.
 3. Treatment according to claim 1 or 2, in whichthe number n of the compound(s) of formula (I) is equal to zero. 4.Treatment according to one of claims 1 to 3, in which the sulphurcompound is a disulphide.
 5. Treatment according to one of claims 1 to4, in which the sulphur compound is DMDS.
 6. Treatment according to oneof claims 1 to 5, in which the sulphur compound is applied in the purestate or in the form of an aqueous emulsion, a microemulsion, a solutionin a biodegradable solvent or a product which is microencapsulated orsupported by a solid.
 7. Treatment according to one of claims 1 to 6, inwhich the compound(s) of formula (I) is(are) applied at a dose between150 and 1000 kg/ha.
 8. Treatment according to claim 7, in which thesulphur compound has no phytotoxic effect.
 9. Treatment according to oneof claims 1 to 8, combined with a treatment (simultaneous or otherwise)with one or more other pesticidal substances.